Flask 15 Ml Of Isopentyl Alcohol example essay topic

Introduction The focus of this experiment was centralized around using the esterification procedure in preparing an ester known as isopentyl acetate. However, in doing so, numerous techniques were used, providing one with the opportunity to withhold a strong sense of the organic chemistry laboratory practice. Isopentyl Acetate, CH 3 COACH 2 CH (CH 3) 2, often referred to as banana oil for its strong banana odor, is a colorless liquid having a melting point of roughly -100^0 C and a boiling point of 143^0 C. Though it is a stable substance, isopentyl acetate is very reactive when mixed with oxidizing agents, strong acids, strong bases, nitrates and alkali metals, acting violently, with the possibility of flammability. In this experimentation, isopentyl acetate, which is an ester, was formed. By combining acetic acid and isopentyl alcohol with the addition of sulphuric acid and heat, an ester, isopentyl acetate was produced. Esters are formed from a reaction of carboxylic acids with alcohols, as is shown below: carboxylic acid alcohol ester water The combination of two molecules joining together to form a much larger molecule, in addition to the loss of water, is a condensation reaction known as esterification. acetic acid isopentyl isopentyl water alcohol acetate By having the reaction mixture as an equilibrium mixture, the equilibrium constant, K, could be calculated, using the concentrations of the reactants and products.

K = [ester] [H 2 O] [alcohol] [acid] The equilibrium constant for esterification is generally less than 4, furthermore, it is easily seen that if one uses one mole of both the carboxylic acid and the alcohol at equilibrium, approximately 2/3 of the ester will be formed. From this information it can also be stated that the highest possibly percentage yield that can be obtained of an ester is roughly 67%. This is a result of the fact that this reaction does not support the formation of an ester. In this experiment, one of the initial reactants, isopentyl alcohol, was used in excess to shift the equilibrium in order to bring Le Chatelier's Principle into play, forcing the reaction to continue to the right, compensating for any lost product.

The easiest way of making an ester is to heat a mixture of carboxylic acid and alcohol with a minimal amount of a sulphuric acid catalyst. A catalyst is 'a chemical substance that, without itself undergoing any permanent chemical change, increases the rate of a reaction'. While the reversible reaction may seem very slow, taking a rather lengthy time to reach equilibrium in the absence of an acid catalyst, it also good to keep in mind that it requires several days for a small amount of sulphuric acid to significantly speed up the grasp of an equilibrium, without changing its position. In order to heat the reaction a reflux procedure took place. Refluxing involves a liquid mixture that is heated, vaporized, and condensed back into its original form, it calls for the reaction to continue at the same temperature of the boiling solvent, and it prevents any of the solvent from being lost to the surrounding atmosphere. Once refluxed, an extraction procedure was used, separating the organic and aqueous phases of the solution, in this particular experiment, the crude ester and the excess acetic acid.

By adding sodium bicarbonate and extra sodium chloride, any acid left over was removed, making the solution basic. A drying agent known as magnesium sulfate, was also used in order to balance out any remnant acid that may have remained throughout the experiment. Finally, the isopentyl acetate was distilled. Distillation is a common procedure used for eliminating a solvent, purifying a liquid or separating the elements of a liquid mixture. A refractive index was used to confirm the identity and purity of the liquid compound, ester. Experimental In order to begin this experiment, a reflux apparatus (figure 1.1) was initially assembled, using a 250 mL Erlenmeyer flask.

To the flask 15 mL of isopentyl alcohol, 20 mL of glacial acetic acid, and 4 mL of concentrated sulphuric acid were added. The contents were then swirled meticulously until all contents were carefully mixed with one another. At this point boiling chips were added and the flask was capped off with a ground glass neck and placed upon a hotplate. Water was then introduced to the condenser and sufficient heat was applied to the mixture to begin the reflux. Figure 1.1: Glassware assembly for reflux The experiment called for the reflux to take place for approximately one hour. Once completed, the solution was cooled in a cold water bath and then transferred into a 250 mL separatory funnel.

In order to achieve a good percentage yield, all contents were to be extracted, therefore 10 mL of cold water was used to rinse the reaction flask further, and remove all the material into the separatory funnel. Once all the rinses were added, an addition 55 mL of cold water was placed in the funnel and closed. The contents were then shaken gently and set aside to delayer. The lower aqueous layer was then drained off and discarded. 25 mL of 5% base was then added to the separatory funnel and swirled until all the carbon dioxide was no longer present. A stopper was then placed, and the funnel was inverted several times, then set aside to delayer once again.

Similarly the lower layer was discarded as waste. This procedure, adding 25 mL of 5% base was repeated several times, checking the basicity of the contents with red litmus paper. Once the litmus paper turned blue, confirming that it was basic 25 mL of distilled water and 5 mL of saturated sodium chloride were added and swirled. The lower aqueous layer was removed and discarded as waste. The organic layer remaining was then placed in a 50 mL Erlenmeyer flask and 3 g of magnesium sulphate were added and swirled.

The magnesium sulphate was used as a drying agent, to dry to ester. The solution was then set aside for 15 minutes for complete drying, if the solution remained cloudy, another gram of magnesium sulphate was added, and once again left to stand. Using a 100 mL distilling flask, a distillation apparatus was set up accordingly (see figure 1.2) The ester was then cautiously decanted into the distillation flask, ensuring that the drying agent was excluded. Boiling chips were then added and the distillation took place.

Figure 1.2: Simple distillation apparatus As the distillation ran through, the ester was released. Once a banana odor or the temperature reached a range of 134-143^0 C, the ester was collected and the product was then placed on a refractometer, where the light source was adjusted to determine the proper refractive index of the substance. Calculations % error = literature value - experimental value x 100 = 1.4003 - 1.4031 x 100 = 0.20% literature value 1.4003% yield = experimental value (g) x 100 = 8.3 x 100 = 46.25% literature value (g) 17.945 For other calculations refer to report form. Discussion The reversible reaction of esterification of isopentyl alcohol and acetic acid to generated 8.3 grams of isopentyl acetate that was close to the theoretical yield, 17.945 grams, giving a 46.25 percent yield. The experimental refractive index of isopentyl acetate attained was very similar to that of the literature values. The experimental value of 1.4035 at 19.2 C, in comparison to the literature value which is 1.4003 at 20 C was fairly close, a 0.20% error.

The percent yield (46%) suggested that the purity of the isopentyl acetate was considerable. The boiling point range for isopentyl acetate was 134-141 C which is very close to the literature value of 142 C. There were numerous sources of error in this experiment, resulting in a loss of product. As we go through the experiment, there are many factors to be taken into account. First off, incorrect decanting from the separatory funnel may have resulted allowed for water to be passed through, making drying nearly impossible. Secondly, in washing out the acid with the sodium bicarbonate, if not done to the fullest, may have resulted in the production of CO 2 gas and pressure build up. Also, in transferring the crude ester to the seperatory funnel, some product may have been lost, or perhaps the drying agent may have absorbed some of the product.

Finally, when distilling the mixture, in order to prevent any cracking of the heated glass, some of the product was left behind in the distillation flask. In determining the purity of the final product, isopentyl acetate, the boiling point has a significant effect on the refractive index. Given that the boiling point of isopentyl alcohol is 130^0 C and isopentyl acetate is 142^0 C, any alcohol that did not undergo the process of esterification is likely to contaminate the final product, as it would come out of the solution at approximately the same time. In the future, this experiment could be performed better by using cautionary procedures in moving the product to the seperatory funnel, refluxing carefully, ensuring that no vapors are released into the atmosphere, and allowing for sufficient drying and separation for a greater amount of time. Keeping these tips in mind, it is likely that this experiment will be much more successful.

Conclusion The experimental refractive index obtained was 1.4035 at 19.2^0 C. The production of isopentyl acetate calculated at the end had a low value in comparison to the literature value. The percent yield of the isopentyl acetate was 46.25%. However, the goal of attaining pure isopentyl acetate was achieved, with boiling points that were relatively close to the literature values indicated in the MSDS, proving this lab to be a success.

Bibliography

Todd, David. (1979) "Experimental Organic Chemistry".
New Jersey: Englewood Cliffs. Prentice Hall pp. 40 - 46 Ryerson University, (2002), Organic Chemistry Laboratory Manual, Faculty of Applied Chemistry and Biology, p.
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